Fix parent transaction linking, add more details to transactions and update to newest Sentry SDK

[janwytze]

In a project where we use this library the span created by the server interceptor was not correctly linked to the parent span from the client. Also requests with no trace id would not get there spans registered, since Sentry will throw away any spans that do not have a transaction. We were also missing some details about the transaction, like the grpc method that was used.

Here is a list of the changes:

• Use StartTransaction instead of StartSpan. This will ensure the span to be registered in Sentry.
• Beside the sentry-trace header, also add the baggage header to grpc requests. This is used for distributed Sentry tracing.
• Update to Sentry SDK 0.27.0.
• Set the Sampled value of a transaction to true when an error occurs, so all errors will contain traces.